Polymer stent with tunable axial and radial flexibility

ABSTRACT

Stents are provided which include geometric segments comprising radial elements and axial elements. Both the radial and axial elements are optionally characterized by a width and a thickness, and the widths and thicknesses of the radial and axial elements are capable of being fixed independently of one another, permitting the axial and radial flexibility of the stent to be controlled independently of one another.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 62/000,864 filed May 20, 2014 by John Howard, et al., which is incorporated by reference herein in its entirety and for all purposes.

FIELD

This application relates to the field of medical devices and medical procedures. More particularly, the application is related to devices and methods for treatment of obstructions of body lumens such as the bile duct.

BACKGROUND

A stent is a medical device that is inserted into a bodily lumen in order to keep the lumen open in the face of factors which tend to close or obstruct the bodily lumen, such as external compressions, internal obstructions, or strictures of the lumen itself. Stents are commonly used in the vascular system, the urinary tract, the esophagus and the biliary tract, among other places. Stents may be made of bare metal, coated metal, or polymer. They may comprise a simple tube or a more complex framework comprising multiple linkages, and they may be implanted acutely or chronically. Some stents are expandable, and can be delivered in a compressed, small-diameter configuration, then expanded radially upon deployment.

In use, a stent should conform to the anatomy of the body lumen, which may be characterized by sometimes complex curvatures and varying internal diameters. In addition, the stent should be rigid enough to resist compression of the lumen and, at the same time, flexible enough to move with the lumen as necessary to accommodate normal patient movement or the natural movement of adjacent tissues. If the stent fails to conform to the anatomy of the lumen, it may allow the lumen to kink, or it may apply too much force to the internal wall of the lumen, causing inflammation or distortion of the lumen (e.g. straightening a normally tortuous lumen). These failures may, in turn, lead to undesirable complications such as scarring, loss of patency, and restenosis.

Polymer stents used in urinary, enteral, esophageal and biliary applications are typically formed as simple tubes, and their ability to conform to the inner walls of lumens is determined by their inner and outer dimensions, their wall thickness, and the stiffness of the polymer(s) used to manufacture the stent. It is difficult or impossible, therefore, for these polymer stents to conform to body lumens in which the curvature or inner diameter varies over the region in which the stent is deployed, or to deform sufficiently to accommodate patient movement while maintaining good, conformal contact with the interior surface of the lumen.

Pancreatic pseudocysts are fluid-filled voids within the pancreas formed by the accumulation of pancreatic enzymes due to occlusion of the pancreatic duct (for example by gallstones) or by traumatic injury. Untreated pseudocysts which do not spontaneously resolve may grow to occupy large volumes and, eventually, become infected, causing significant complications including pain and sepsis. Current treatments for pseudocysts generally involve forming an anastomosis (i.e. a man-made lumen) between the pancreas and the stomach, bridging the pseudocyst to permit its drainage into the digestive tract so it can be removed. Anastomoses formed to treat pseudocysts are typically bridged by stents which are delivered by endoscopes threaded through the esophagus and into the stomach. However, currently used plastic stents which are delivered endoscopically are not capable of expanding to the wide diameters necessary to effectively drain pancreatic pseudocysts, and in some instances multiple tubes are used to maintain the patency of the pseudocyst drainage paths. Braided or woven bare metal stents are sometimes used instead of polymer stents to provide the expansion necessary for treatment of pseudocysts. However, bare metal stents can be significantly more expensive than plastic stents and may cause tissue irritation.

SUMMARY

The present disclosure, in its various aspects, provides cost-effective stents which are capable of significant compression and re-expansion, and are flexible enough to accommodate patient movement while applying the radial force necessary to maintain flow through body lumens.

In one aspect, the present disclosure relates to a biliary stent comprising a plurality of geometric segments that include at least one radial element that extends about a circumference of the biliary stent and has a width and a thickness and at least one axial element extending along at least part of the length of the stent, the axial element also having a width and a thickness. The biliary stent optionally comprises a shape memory polymer, and is configured to move between a compressed configuration and an expanded configuration which differs from the compressed configuration in that at least one of a diameter of the stent and a length of the stent is increased in the expanded configuration. The widths and/or the thicknesses of the axial and radial elements can be modified independently, thereby allowing independent control of the axial and radial stiffness of the stent. The radial element may be a hoop or a coil spring, while the axial element may be a strut or a tube. As discussed above, the width and/or the thickness of the axial and/or the radial elements may vary along the length of the stent (e.g. greater at the ends, less in the middle), thereby varying the radial and/or axial stiffness of the stent along its length (e.g. stiffer at the ends, more flexible in the middle). Also as discussed above, the fixing temperature of the shape memory polymer used in the stent is optionally between 37° and 48° Centigrade. In some embodiments, the biliary stent is used for treatment of pancreatic pseudocyst, for instance as part of a kit in which the stent is in the compressed form, while in other embodiments the stent moves from the compressed configuration to the expanded configuration when placed in the body of a patient.

In another aspect, the present disclosure relates to a biliary stent comprising a shape memory polymer which is formed as plurality of hoops that extend radially about a circumference of the stent, and a plurality of struts disposed between and connecting the hoops. Each hoop has a hoop width and a hoop thickness, and each strut has a strut width and a strut thickness. The widths and/or thicknesses of the hoops and struts may be different from one another, and any of the hoop width, hoop thickness, strut width and strut thickness can vary over the length of the stent (e.g. greater at the ends, smaller at the middle, so the stent is stiffer at the ends than in the middle). The stent, in some embodiments, has a compressed configuration in which it exhibits a first diameter and a first length as well as an expanded configuration with a second diameter and a second length. At least one of the diameter and the length is greater in the expanded configuration than in the compressed configuration; in some cases, the length is greater in the compressed configuration while the diameter is greater in the expanded configuration. The hoops and struts, in various embodiments, form a plurality of diamond-shaped voids. The shape memory polymer preferably has a fixing temperature between 37° and 43° Centigrade, though the fixing temperature may be as high as 48° Centigrade in some embodiments, as temperatures that high can be tolerated without tissue damage for short periods of time. In some embodiments, the biliary stent is used for treatment of pancreatic pseudocyst, for instance as part of a kit in which the stent is in the compressed form, while in other embodiments the stent moves from the compressed configuration to the expanded configuration when placed in the body of a patient.

In another aspect, the present disclosure relates to a biliary stent comprising a plurality of helical segments and at least one non-helical segment which is located at an end of the implant or interposed between multiple helical segments. The stent includes a shape-memory polymer and can be moved from a compressed configuration into an expanded configuration in which at least one of a diameter of the stent and a length of the stent is increased relative to the compressed configuration. In some cases, the non-helical segment is a retentive tang disposed at an end of the stent, while in other cases the non-helical segment is a tube or a strut.

In yet another aspect, the present disclosure relates to a method of treating a patient in need of biliary stenting which includes providing a stent according to any of the aspects presented above. The stent is provided in the compressed configuration to an anastomosis between the stomach and pancreas and is then expanded to its memorized shape, for example by contact with a balloon with inflated with heated saline. The stent is optionally delivered through the working channel of an endoscope on a balloon, and is expanded beyond its memorized shape by expanding the heated balloon, optionally with heated saline, and allowing it to “freeze’ at its overexpanded shape.

DETAILED DESCRIPTION

Aspects of the disclosure are described below with reference to the following drawings in which like numerals reference like elements, and wherein:

FIG. 1 depicts a stent according to certain embodiments of the disclosure.

FIG. 2 depicts a stent according to certain embodiments of the disclosure.

FIG. 3 depicts a stent according to certain embodiments of the disclosure.

Unless otherwise provided in the following specification, the drawings are not necessarily to scale, with emphasis being placed on illustration of the principles of the disclosure.

In general, stents of the disclosure are hollow, generally tubular bodies comprising two or more geometric segments, each segment in turn comprising (i) a radial element which extends circumferentially, and (ii) an axial element which extends along all or part of the length of the stent. Stents of the disclosure are self-expanding and typically include a shape memory polymer such as polycyclooctene, which preferably has a fixing temperature that is greater than or equal to body temperature (37° Centigrade). Both the radial and axial elements of the stents are characterized by a thickness defined as the difference between the inner and outer diameters of the stent occupied by polymer when the stent is fully expanded, and a width defined as the distance across the element, as measured when the stent is fully expanded. The thickness and width of the radial and axial elements can be adjusted independently of one-another, advantageously permitting the radial flexibility and axial stiffness of the stent to be determined independently. In other stents currently in use, and particularly biliary stents, it has not been possible to modify one characteristic without modifying the other inasmuch as currently-used stents are generally tubular and homogeneous in structure.

Shape memory materials, and specifically shape memory polymers, are the preferred materials for fabricating stents according to various embodiments of the present disclosure. Structures made using shape memory polymers have “memorized” shapes which are fixed, for example, by cross-linking during the stent forming process. These structures spontaneously revert to their memorized shapes when they are exposed to temperatures above the polymer's “fixing temperature,” unless external stresses are applied to force the structures into different shapes. In stents of the present disclosure, shape memory materials advantageously permit either expansion or contraction, thereby permitting the stents to be removed in lower-volume configurations, while achieving higher-volume configurations when deployed. For instance, a stent according to the present disclosure may have memorized shape which is characterized by relatively small diameter (i.e. it is compressed). The stent according to this embodiment may be expanded by inflating it with a heated balloon and allowing the balloon and the stent to cool. When removal of the stent is desired, a balloon may be threaded through the expanded stent, heated and deflated, allowing the stent to resume its memorized shape.

The stents described herein can be adapted for use in any setting where stenting may be desired, including the esophagus, the duodenum, the ureter, or the biliary system by altering the dimensions and mechanical properties of the stent. The examples provided herein focus on biliary stents adapted for treatment of pancreatic pseudosysts. Stents suitable for this application are generally delivered through tortuous body passages in the digestive system to the pseudocyst via the working channel of an endoscope, and must expand to a diameter that is substantially greater than the inner diameter of the working channel in order to reliably and permanently bridge the pseudocyst. Accordingly, a stent with high axial flexibility is particularly desirable to navigate the tight curves that occur as the stent is threaded, via the working channel, through the esophagus and stomach and is then extended out of the working channel.

Referring now to FIG. 1, an exemplary stent 100 according to certain embodiments of the disclosure is constructed to provide tunable axial and radial flexibility. The stent 100 includes a plurality of repeating geometric elements, each element including axial elements referred to as struts 105 which are characterized by a strut width w_(s) and a strut thickness t_(s). The struts 105 connect radial elements referred to as hoops 110, which are in turn characterized by a hoop width w_(h) and a hoop thickness t_(h). In the embodiment of FIG. 1, each hoop 110 is connected to four struts 105, two on each side, which struts are generally spaced 180 degrees apart from one another and which are offset by 90 degrees on opposite sides of the hoop 110. This arrangement allows the stent 100 to exhibit substantially the same axial flexibility about its entire circumference: the skilled artisan will appreciate that the struts 105 will tend to resist out-of-plane bending, and geometries in which the struts 105 are offset from one another will reduce the resistance to bending in any single plane. Alternatively, while not necessarily preferred, in some embodiments the struts 105 are not radially offset from one another, and the resistance to bending is maximized in a first plane defined by the struts 105 while being minimized in a second plane perpendicular to the first plane. While not wishing to be bound to any theory, in general, the radial offset of the struts is a determinant of the relative stiffness or flexibility in various axial planes, and a specific radial offset may be selected, in some cases, to achieve a desired ratio of axial stiffness between two or more different axial planes.

In the embodiment of FIG. 1, the struts 105 contribute to the axial stiffness of the stent 100, and can be made stiffer (i.e. more resistant to bending) by increasing either or both of the strut width w_(s) and the strut thickness t_(s) and/or by shortening the length of the struts 105. Alternatively, the struts 105 can be made more flexible (i.e. less resistant to bending) by decreasing either or both of the strut width w_(s) and the strut thickness t_(s) and/or increasing the length of the struts 105. In a similar fashion, the hoops 110 contribute to the radial stiffness (i.e. the resistance to radial compression) of the stent, which can be increased by increasing the hoop width w_(h) and/or hoop thickness t_(h), and can be decreased by decreasing the hoop width w_(h) and/or hoop thickness t_(h). This arrangement advantageously permits the dimensions of the struts 105 and the hoops 110 to be modified independently of one-another, allowing the axial stiffness and radial stiffness of the stent 100 to be tuned independently of one another. For instance, the hoop width of the stent 100 can be increased without affecting the dimensions of the strut 105, thereby permitting an increase in the radial stiffness of the stent 100 without affecting its axial stiffness.

In the embodiment of FIG. 1, the struts 105 and hoops 110 define a repeating pattern of roughly diamond-shaped voids 115. These voids 115 give the stent 100 a wide range of motion to deform axially and radially by reducing the mechanical interference between adjacent hoops when the stent 100 is bent; the configuration of FIG. 1 is capable of deflecting about 270° into a ¾ circular shape, which advantageously permits a stent 100 of the present disclosure to be navigated through and deployed into tortuous body lumens.

The incorporation of diamond-shaped voids 115 can help prevent permanent deformation by helping to ensure that the tensile stress that is applied to any single portion of the stent 100 during axial expansion does not exceeded the yield stress of the structure. The diamond-shaped voids 115 themselves are capable of deforming to some degree, preventing the concentration of stress on the struts 105 which could potentially damage the stent 100.

Other embodiments of the disclosure, it should be noted, do not necessarily include diamond-shaped voids 115; instead, the hoops 110 may be generally parallel to one another. While not wishing to be bound to any theory, the ability of the stent 100 to deflect about various curvatures is constrained by mechanical interference between adjacent hoops, and increasing an angular distance between adjacent hoops will tend to increase the ability of the stent 100 to deflect. Factors which affect the angular distance between individual hoops include the hoop width w_(h) and hoop diameter as well as the length of the struts 105.

Embodiments of the disclosure, including those shown in FIG. 1, preferably incorporate a shape-memory material to facilitate expansion of the stent 100 into its deployed configuration after delivery to the site of treatment in a compressed configuration. The compressed configuration of the stent 100 is characterized by a maximum outer diameter and/or a maximum length which is less than the maximum outer diameter and/or length in its deployed configuration. The stent 100 is generally packaged and introduced into the body of a patient in the compressed configuration, for example through a working channel of an endoscope and/or crimped over a delivery catheter.

To deploy the stent 100, it is placed in its desired location within the patient's body and expanded. To treat pancreatic pseudocysts, the stent is advanced through the working channel of an endoscope threaded through the esophagus to the stomach at a site of an anastomosis. The stent 100 is then expanded by the user, for example by inflation of a balloon underlying the stent 100 with heated saline or direct irrigation of the stent with heated fluid, thereby increasing the temperature of the stent 100 to at least the fixing temperature of the polymer used. The expansion of the stent may be aided by mechanical means (for example, the force applied by the expanded balloon). It is generally desirable (though not required) that, irrespective of the heating means used, the expansion of the stent 100 be fully controllable by a user to minimize the risk of incorrect deployment of the stent.

Once deployed, the stent 100 will expand towards its expanded configuration, preferably achieving even, circumferential contact across its length with the inner wall of the lumen. A stent 100 according to various embodiments of the disclosure may be made in a variety of sizes, and is preferably sized such that a maximum outer diameter of the stent 100 when in the fully expanded configuration is slightly greater than an inner diameter of the body lumen or anastomosis into which the stent 100 will be placed.

Referring again to FIG. 1, the stent 100 preferably includes one or more retention features such as antimigration wings 120. The antimigration wings 120 preferably define the widest portions of the implant in its expanded configuration, extend about at least a portion of the circumference of the stent 100, and are positioned at the ends of the stent 100. When deployed, the antimigration wings 120 apply an outward radial force to the inner wall of the lumen, helping the stent 100 to remain in a fixed position within the body lumen. When the stent 100 is used to bridge an anastomosis, the retentive wings will expand to secure the stent about the walls of the anastomosis. Alternatively or additionally, the retention feature may be a region of increased diameter at or near the end of the stent. Regions of increased diameter at the ends of the stent 100 are particularly useful for applications such as the treatment of pancreatic pseudocysts where the stent will bridge an anastomosis having a relatively narrow diameter which is flanked on both sides by spaces having substantially larger diameters. More generally, retention features are useful when the stent 100 is used to bridge spaces of similar diameter, as the features interact mechanically with the tissue on either side of the stent when deployed.

The use of a shape memory polymer to form the stent 100 is preferred when the stent 100 will include a retention feature such as antimigration wings 120, as it is difficult to deploy structures which extend beyond the diameter of the rest of the stent using only mechanical means such as a balloon.

Turning to FIG. 2, in an alternative embodiment, a stent 200 comprises a plurality (e.g. 2, 3, 4, 5 etc.) of helical elements 205 and at least one tubular element 210 interposed between the helical elements 205 and, preferably, disposed at each end of the stent 200. In this embodiment, again, the stent 200 comprises a shape-memory polymer such as polycyclooctane, and is able to be crimped into a compressed configuration and to expand, aided by heating and/or mechanical expansion, into an expanded configuration in which at least one of a diameter and a length of the stent 200 is increased relative to the compressed configuration. And, as described above, the stent 200 also includes a retention feature such as antimigration wings 215, which function as described above.

The use of helical elements 205 and tubular elements 210 advantageously simplifies the manufacture of the stent 200, which can be manufactured by molding or extruding a tubular blank and spiral cutting to form the helical elements 205; the tubular elements 210 are formed between the helical cuts.

The stents described above have generally utilized helical and axial elements which have rectangular or polygonal cross-sections, i.e. characterized by distinct width and thickness. However, elements with other cross-sectional geometries are also within the scope of the disclosure. In certain embodiments, the stent comprises at least one member having a circular cross-section, such as the coil spring shown in FIG. 3. Where a coiled spring element is used, both axial and radial stiffness are determined in part by the cross-sectional diameter of the coiled polymer—with thicker coils generally being stiffer both axially and radially. In addition, radial flexibility is determined in part by the diameter of the coil in the fully expanded configuration, with larger diameter coils being generally stiffer radially. Axial flexibility is determined in part by the number of coils, with more coils generally resulting in an implant with greater axial stiffness. One advantage of coiled spring members formed from shape memory polymers in accordance with these embodiments is the relative ease with which the axial and radial stiffness of the coil can be altered: the maximum diameter can be adjusted simply by winding or unwinding the coil in its expanded configuration, then exposing the stent to a temperature at or above the fixing temperature of the shape memory polymer in order to “set” the adjusted diameter, thereby increasing or reducing the radial flexibility of the stent. In addition, the number of coils can be reduced simply by cutting off a portion of the implant and/or by stretching or compressing the coil axially in its expanded configuration, then exposing the stent to a temperature above the fixing temperature to “set” the stent.

An additional advantage of a coiled spring member is the ease with which an anti-migration feature can be formed: as shown in FIG. 3, a portion of the coil on either end of the implant can simply be bent outward or backward, thereby forming a tang which extends away from the remaining coils of the stent and which applies a radially outward retentive force to the inner surface of the body lumen when deployed.

The various embodiments of the present disclosure share a number of important advantages relative to other stents for use in biliary, renal, enteric or esophageal applications. First, the use of separate axial and radial elements along with shape-memory polymers enables the creation of stents which exhibit a high degree of radial stiffness combined with high axial flexibility, permitting the stent to move with the patient and to be threaded through tortuous body passages for delivery in a narrow configuration that can pass through the working channel of an endoscope, then expand to fill a lumen that is larger in diameter than the endoscope working channel. Second, embodiments of the disclosure make it possible to vary the mechanical characteristics of the stent across its length. For instance, the radial stiffness may be increased at the ends of the implant relative to the center by increasing the width or thickness of radial elements at the ends relative to those in the center. Such an arrangement would improve the engagement of retention features disposed at the ends of the stent with the surrounding tissue, thereby improving retention of the stent, while preserving the flexibility of the stent in its center to accommodate curvature and movement.

In certain cases, as discussed above, a tubular blank is formed into a stent according to any of the embodiments discussed herein by laser cutting or punch cutting; alternatively, stents are formed by injection molding or by fusing of individual polymer filaments. The dimensions of the stent in the expanded diameter are established by holding the stent at its expanded diameter and length and heat-setting it at a temperature above the fixing temperature of the shape memory polymer used. Thereafter, the stent is crimped into its compressed configuration directly or by passage through sequentially smaller dies.

Stents according to the different embodiments of the disclosure preferably incorporate one or more shape memory polymers having fixing temperatures above body temperature. The polymers are generally biocompatible, and are optionally, but not necessarily, biodegradable. Exemplary biodegradable shape memory polymers with suitable fixing temperatures include, without limitation, oligo(ε-caprolactone)diol (“OCL”), oligo(p-dioxanone)diol (“PDD”), poly(p-dioxanone)/poly(ε-caprolactone) block copolymers, and other polymer compositions that include one or more of OCL and PDD. Non-biodegradable shape-memory polymers suitable for use in embodiments of the present disclosure include, without limitation, polycyclooctane.

The phrase “and/or,” as used herein should be understood to mean “either or both” of the elements so conjoined, i.e., elements that are conjunctively present in some cases and disjunctively present in other cases. Other elements may optionally be present other than the elements specifically identified by the “and/or” clause, whether related or unrelated to those elements specifically identified unless clearly indicated to the contrary. Thus, as a non-limiting example, a reference to “A and/or B,” when used in conjunction with open-ended language such as “comprising” can refer, in one embodiment, to A without B (optionally including elements other than B); in another embodiment, to B without A (optionally including elements other than A); in yet another embodiment, to both A and B (optionally including other elements); etc.

The term “consists essentially of means excluding other materials that contribute to function, unless otherwise defined herein. Nonetheless, such other materials may be present, collectively or individually, in trace amounts.

As used in this specification, the term “substantially” or “approximately” means plus or minus 10% (e.g., by weight or by volume), and in some embodiments, plus or minus 5%. Reference throughout this specification to “one example,” “an example,” “one embodiment,” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the example is included in at least one example of the present technology. Thus, the occurrences of the phrases “in one example,” “in an example,” “one embodiment,” or “an embodiment” in various places throughout this specification are not necessarily all referring to the same example. Furthermore, the particular features, structures, routines, steps, or characteristics may be combined in any suitable manner in one or more examples of the technology. The headings provided herein are for convenience only and are not intended to limit or interpret the scope or meaning of the claimed technology.

Certain embodiments of the present disclosure have been described above. It is, however, expressly noted that the present disclosure is not limited to those embodiments, but rather the intention is that additions and modifications to what was expressly described herein are also included within the scope of the disclosure. Moreover, it is to be understood that the features of the various embodiments described herein were not mutually exclusive and can exist in various combinations and permutations, even if such combinations or permutations were not made express herein, without departing from the spirit and scope of the disclosure. In fact, variations, modifications, and other implementations of what was described herein will occur to those of ordinary skill in the art without departing from the spirit and the scope of the disclosure. As such, the disclosure is not to be defined only by the preceding illustrative description. 

What is claimed is:
 1. A biliary stent, comprising: a plurality of helical segments and at least one non-helical segment interposed between adjacent helical segments or disposed at an end of the biliary stent, wherein the biliary stent comprises a shape memory polymer and is moveable from a compressed configuration to an expanded configuration in which at least one of a diameter of the biliary stent and a length of the biliary stent is increased relative to the compressed configuration.
 2. The biliary stent of claim 1, wherein the at least one non-helical segment is a retentive tang disposed at an end of the stent.
 3. The biliary stent of claim 1, wherein the at least one non-helical segment is one of a tube and a strut.
 4. The biliary stent of claim 1, wherein the fixing temperature of the shape memory polymer is greater than or equal to 37° Centigrade.
 5. The biliary stent of claim 1, wherein the biliary stent assumes the expanded configuration when disposed within a body lumen of a patient.
 6. A biliary stent, comprising: a plurality of geometric segments, each of the plurality of geometric segments comprising at least one radial element extending about a circumference of the biliary stent, the at least one radial element characterized by at least one of a width and a thickness; and at least one axial element extending along at least a portion of a length of the biliary stent, the at least one axial element characterized by at least one of a width and a thickness.
 7. The biliary stent according to claim 6, wherein (a) the biliary stent comprises a shape-memory polymer, (b) the biliary stent is configured to move between a compressed configuration characterized by a compressed diameter and a compressed length and an expanded configuration characterized by an expanded diameter and an expanded length, at least one of which is greater than the compressed diameter or the compressed length, respectively, and (c) at least one of the width and the thickness of the at least one radial element can be modified without affecting the axial flexibility of the biliary stent.
 8. The biliary stent according to claim 7, wherein the fixing temperature of the shape memory polymer is greater than or equal to 37° Centigrade.
 9. The biliary stent according to claim 7, wherein the biliary stent assumes the expanded configuration when disposed within a body lumen of a patient, the expanded diameter is greater than the compressed diameter and the expanded length is less than or equal to the compressed length.
 10. The biliary stent according to claim 6, wherein the at least one radial element is one of a hoop and a coil spring.
 11. The biliary stent according to claim 6, wherein the at least one axial element is one of a strut and a tube.
 12. The biliary stent according to claim 6, wherein at least one of the width of the radial element, the thickness of the at least one radial element, the width of the at least one axial element and the thickness of the at least one axial element varies along the length of the biliary stent.
 13. A biliary stent, comprising: a plurality of hoops extending radially about a circumference of the biliary stent, each of the plurality of hoops having a hoop width and a hoop thickness; and a plurality of struts disposed between and connecting the hoops, each strut having a strut width and a strut thickness, wherein the biliary stent includes a shape memory polymer.
 14. The biliary stent of claim 13, wherein the biliary stent has a compressed configuration characterized by a first diameter and a first length and an expanded configuration characterized by a second diameter and a second length, wherein at least one of the second diameter and the second length is greater than the first diameter or the first length, respectively.
 15. The biliary stent of claim 14, wherein the biliary stent assumes the expanded configuration when disposed within a body lumen of a patient, the second diameter is greater than the first diameter, and the second length is less than or equal to the first length.
 16. The biliary stent of claim 13, wherein the plurality of hoops and the plurality of struts form a plurality of diamond-shaped voids.
 17. The biliary stent of claim 13, wherein the hoop width is different than the strut width.
 18. The biliary stent of claim 13, wherein the hoop thickness is different than the strut thickness.
 19. The biliary stent of claim 13, wherein at least one of the hoop width, hoop thickness, strut width and strut thickness varies along a length of the stent.
 20. The biliary stent of claim 13, wherein the shape-memory polymer has a fixing temperature greater than or equal to 37° Centigrade. 